avfilter/vf_rotate: use vsub for output plane height calculation

Output plane height used horizontal instead of vertical subsampling.
This is just cosmetic change as filter does not support formats where
vertical subsampling does not match horizontal one.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_rotate.c

@@ -337,7 +337,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         int inw  = FF_CEIL_RSHIFT(inlink->w, hsub);
         int inh  = FF_CEIL_RSHIFT(inlink->h, vsub);
         int outw = FF_CEIL_RSHIFT(outlink->w, hsub);
-        int outh = FF_CEIL_RSHIFT(outlink->h, hsub);
+        int outh = FF_CEIL_RSHIFT(outlink->h, vsub);
 
         const int xi = -outw/2 * c;
         const int yi =  outw/2 * s;